class MaxStack(Stack):
def __init__(self) -> None:
super().__init__()
self.max_stack = Stack()
def peek(self):
return super().peek()
def push(self, item: Any):
if self.max_stack.empty():
self.max_stack.push(item)
else:
self.max_stack.push(max(item, self.max_stack.peek()))
super().push(item)
def pop(self):
self.max_stack.pop()
return super().pop()
def max(self):
"""
Получить максимальный элемент. Не извлекает его из стека.
"""
return self.max_stack.peek()
def empty(self):
return super().empty()
def __len__(self):
return super().__len__()
def __bool__(self):
return super().__bool__()
def convert_infix_to_prefix(infix_expression):
reverse = reverse_string(infix_expression)
operators = Stack()
prefix_expr = []
ops = '(+-*/**)'
expr_list = list(reverse)
for token in expr_list:
if token not in ops:
prefix_expr.append(token)
elif token == ')':
operators.push(token)
elif token == '(':
while operators.peek() != ')':
prefix_expr.append(operators.pop())
operators.pop()
else:
while (not operators.is_empty()
) and precedence[operators.peek()] > precedence[token]:
prefix_expr.append(operators.pop())
operators.push(token)
while not operators.is_empty():
prefix_expr.append(operators.pop())
return reverse_string(''.join(prefix_expr))
class TestStack(unittest.TestCase):
def setUp(self):
self._stack = Stack()
def test_pop_from_empty_stack_raises_index_error(self):
self.assertRaises(IndexError, self._stack.pop)
def test_pop_from_empty_stack_which_had_items_raises_index_error(self):
self._stack.push(1)
self._stack.pop()
self.assertRaises(IndexError, self._stack.pop)
def test_pop_returns_items_in_order(self):
self._stack.push(3)
self._stack.push(2)
self._stack.push(1)
assert (self._stack.pop() == 1)
assert (self._stack.pop() == 2)
assert (self._stack.pop() == 3)
def test_peek_returns_top_item(self):
self._stack.push(2)
self._stack.push(1)
assert (self._stack.peek() == 1)
def test_peek_leaves_item_on_stack(self):
self._stack.push(1)
assert (self._stack.peek() == 1)
assert (self._stack.pop() == 1)
def test_pop():
my_stack = Stack()
my_stack.push(0)
my_stack.push(1)
popped = my_stack.pop()
assert popped == 1
assert my_stack.peek() == 0
def check_parentheses(symbol_string):
s = Stack()
balanced = True
index = 0
matcher = {
'}': '{',
']': '[',
')': '(',
}
while index < len(symbol_string) and balanced:
symbol = symbol_string[index]
if symbol in ['(', '[', '{']:
s.push(symbol)
elif symbol in [')', ']', '}']:
if s.is_empty() or matcher[symbol] != s.peek():
balanced = False
else:
s.pop()
index = index + 1
if balanced and s.is_empty():
return True
else:
return False
def convert_infix_to_postfix(infix_expr):
op = Stack()
postfix = []
infix = list(infix_expr)
for index in range(len(infix)):
if infix[index] in ops:
while (not op.is_empty()) and precedence[op.peek()] >= precedence[infix[index]]:
if op.peek() == '(':
op.pop()
else:
postfix.append(op.pop())
if infix[index] != ')':
op.push(infix[index])
elif infix[index] != ' ':
postfix.append(infix[index])
while op.size() > 0:
postfix.append(op.pop())
print(''.join(postfix))
def convert_infix_to_postfix_new(infix_expr):
op = Stack()
postfix = []
infix = list(infix_expr)
for index in range(len(infix)):
token = infix[index]
if token not in ops:
postfix.append(token)
elif token == '(':
op.push(token)
elif token == ')':
while op.peek() != '(':
postfix.append(op.pop())
op.pop()
else:
while (not op.is_empty()) and precedence[op.peek()] >= precedence[infix[index]]:
postfix.append(op.pop())
op.push(token)
while not op.is_empty():
postfix.append(op.pop())
print(''.join(postfix))
def test_peek():
my_stack = Stack()
my_stack.push(0)
my_stack.push(1)
assert my_stack.peek() == 1
def test_stack_peek(given, peek):
stack = Stack(given)
assert stack.peek().value == peek